1. Field of the Invention
The present invention relates to a character recognition method, in particular, to a character recognition method of comparing input image data with characters in a predetermined dictionary and recognizing a character indicated by the input image data.
2. Description of the Related Art
Recently, OCR (Optical Character Reader) devices, which optically read a pattern such as a character, a mark and the like, are used in various arts. For example, in a semiconductor device manufacturing process, numerals, letters, marks and the like, which are printed on a semiconductor wafer, are optically read by the OCR device, and the characters printed on the wafer are recognized from the image data read by the OCR device. Consequently, for example, a preferable condition of a specific process in the manufacturing process of the semiconductor device is established and management of the wafer which may be reprocessed is carried out by using the recognized characters. In the above description, an image of the characters printed on the semiconductor wafer may be taken by a camera, and the image data may then be changed into a binary code by a binary processing circuit. Furthermore, the digital image data of the binary code may be changed into a dot-matrix form by a dot-matrix processing circuit, after which a character recognition process can be carried out.
In a conventional character recognition method, input image data in a dot-matrix form is compared with a predetermined dictionary (for example, compared by using a pattern matching method), that is, the dot-matrix data of the image data is successively compared with dot-matrix data of each of the character patterns which are previously provided as reference characters in the dictionary. Consequently, a character, having the smallest number and lower than a predetermined number (which is a threshold value) of different dots between dot-matrix data of each of character patterns and the dot-matrix data of the image data, is recognized as the character indicated by the input image data.
Note, in the manufacturing process of semiconductor devices, for example, a semiconductor wafer is frequently nipped and removed by using a pincette and the like, so that the characters printed on the wafer may be damaged by the pincette and the like, and a flaw may be formed on the characters on the wafer.
Additionally, dust may adhere to the surface of the wafer where the characters are printed, so that a part of the characters of the wafer are not visible. As described above, when the characters on the wafer are obscured by a flaw, a missing portion, dust and the like, the characters printed on the wafer may not be correctly recognized from the input image data.
In consideration of the above, a conventional character recognition method is proposed, wherein complicated image processes are carried out in the steps of taking an image of characters by a camera, changing an analog signal of the image data into a binary code by a binary processing circuit, and changing the digital image data of the binary code into a dot-matrix form by a dot-matrix processing circuit, in order to decrease the negative influences due to a flaw and the like, and increasing the accurcy of the character recognition. In the above conventional character recognition method, a plurality of special hardware is required to decrease the negative influence of the flaw and the like. Consequently, though a highly accurate character recognition can be possible, the cost for the character recognition would be very expensive.